1. Field of the Invention
This invention relates generally to a method of enhancing lean tissue mass in a subject by administering to the subject calcium, and optionally vitamin D. In another embodiment, the present invention relates to a method of enhancing bone mineral content in a physically active subject by administering to the subject calcium, and optionally vitamin D.
2. Background Art
One of the many numerous benefits of physical activity is increased bone mineral content (BMC)/bone density. There is strong evidence that moderate levels of weight-bearing physical activity are positively correlated to increased BMC in cross-sectional (Gutin et al. "Can vigorous exercise play a role in osteoporosis prevention?" Osteoporosis Int 1992; 2:55-69) and prospective studies (Gutin et al. and Menkes et al. "Strength training increases regional bone mineral density and bone remodeling in middle-aged and older men." J Appl Physiol 1993;74:2478-2484; Nelson et al. "A one year walking program and increased dietary calcium in postmenopausal women: Effects on bone." Am J Clin Nutr 1991;53:1303-131; and Krall et al. "Walking is related to bone density and rates of bone loss." Am J Med 1994;96:20-26). The vast majority of these studies have been done with middle aged sedentary adults who are at risk for osteoporosis and other bone-related injuries (See, e.g., Gutin et al. and, Menke et al.). There is therefore little doubt that moderate activity and increases in exercise in sedentary subjects promote positive changes in bone density.
As the literature in this area has progressed, investigators have also begun to investigate the relationship between BMC and consistent, vigorous activity. Much of the work in this area has focused on female athletes and activity-induced amenorrhoea. In these investigations, studies typically find a negative or no relationship between physical activity and BMC in female amenorrheic athletes. (Suominen H. "Bone mineral density and long term exercise: An overview of cross-sectional athlete studies." Sports Med 1993; 16:316-330 and Marcus et al. "The role of physical activity in bone mass regulation". Advances Sports Med Fitness 1988;1:63-82). The mechanism presumed to be responsible for the lowered BMC of highly trained female athletes is a low level of endogenous estrogen. (Suominen H.)
Most recently, however, there have been reports of lowered BMC/bone densities in highly trained male athletes as well. (Bilanin et al. "Lower vertebral bone density in male long distance runners." Med Sci Sports Exer 1989;21:66-70; MacDougall et al. "Relationship among running mileage, bone density, and serum testosterone in male runners." J Applied Physiol 1992;73: 1165-1170; Hetland et al. "Low bone mass and high bone turnover in male long distance runners." J Clin Endocrinol Metab 1993;77:770-775; and Rico et al. "Body composition in postpubertal boy cyclists." J Sports Med Phys Fitness 1993;3:278-281). One study (Hetland et al.) reported a negative correlation between weekly distance run and bone mineral density at several sites in male long distance runners. Bone turnover parameters were 20-30% higher in the elite runners. Because sex hormone metabolism is thought to be associated with bone density in female athletes, this was assessed in this sample of males but found to be unrelated to running activity. This study did not exclude the possibility that the lower bone density content of elite runners versus non-runners was attributable to the lower body weight of the elite runners. Additionally, there is some evidence that risk of BMC loss may be particularly high in late adolescence when bone formation is likely to be still occurring. (Rico et al.) In a study of amateur male bicyclists 15-19 years of age engaged in training that could not be described as intense (mean training=10 hours per week), total BMC and bone density were significantly lower than in sedentary controls. Because low bone density is an etiologic factor for stress fractures in athletes (Myburgh et al. "Low bone density is an etiologic factor for stress fractures in athletes." Ann Intem Med 1990;113:754-759) and stress fractures are extremely common in athletic sports (Johnson et al. "Stress fractures of the femoral shaft in athletes--More common than expected: A new clinical test." Am J Sports Med 1994;22:248-256), any reductions in BMC should be viewed with concern. Indeed, one should be observing increases in bone density in early and late adolescent athletes as this is a time of rapid bone formation. (Matkovic et al "Factors that influence bone mass formation: A study of calcium balance and the inheritance of bone mass in adolescent females." Am J Clin Nutr 1990;52:878-888.)
This phenomenon of lower bone mineral content in physically active individuals had not previously been correlated with calcium intake or calcium loss. For example, Hetland et al. concluded from their investigations that calcium consumption had no significant influence in their results which showed a negative correlation between the extent of exercise and bone mineral content.
Another benefit of certain intensity levels of and/or duration levels of physical activity is an increase in lean tissue mass (i.e. muscle). Some individuals, however, suffer decreased lean tissue mass as a result of a number of factors, including extremely high intensity levels of and/or high duration levels of physical activity. However, no relationship between decreasing lean tissue mass loss or improving lean tissue mass increase and calcium has been previously studied or established.
There exists a need in the art, therefore, to solve the problem of a lower bone mineral content associated with physical activity. There also exists a need to enhance lean tissue mass, preferably in physically active individuals.
This invention solves the problem of the prior art by providing a method to enhance the bone mineral content in physically active individuals by either decreasing a loss of bone mineral content in physically active individuals or optimally, to increase the bone mineral content of physically active individuals, by administering to those individuals calcium. This invention also provides a method of either decreasing a loss of lean tissue mass in preferably physically active individuals or optimally, to increase the lean tissue mass of preferably physically active individuals, by administering to those individuals calcium.